Keeping the output voltage of high-voltage electrical equipment, such as transformers, for example, within allowed or desired ranges depending on load circumstances has conventionally been done by means of changing the transformation ratio of said electrical equipment, such that the ratio between the voltages of the primary winding and of the secondary winding of said electrical equipment changes accordingly. To that end, the high-voltage electrical equipment is provided with a device called a tap changer, which can consist of an off-load or on-load tap changer, i.e., the changeover of taps can be done with the electrical equipment de-energized or energized. The tap changer device increases or reduces the number of turns of the primary winding, thereby changing the transformation ratio, or in other words changing the voltage in the secondary winding.
Use of the on-load tap changer device is common in electrical equipment, such as power transformers, for example, the service of which cannot be interrupted without seriously jeopardizing operation of the distribution system and with the subsequent nuisance for users of the distribution grid.
There are tap changer devices today, such as the one mentioned in patent document WO2013156268A1, for example, which discloses an on-load tap changer comprising switching means (vacuum interrupters) and tap selector means driven by a motor. These means are mounted vertically on a support plate, each of them on each side of the support plate, such that transmission of the action of the motor to said means is carried out by intermediate elements, such as a camshaft, a threaded spindle, sliding carriages, etc. These intermediate elements are mechanically linked with the switching means and tap selector means by means of linear motion, i.e., said elements transform rotational movement of the motor into linear movement to actuate the switching means and tap selector means.
The need for using all these intermediate elements involves the drawback of the volume the tap changer device adopts, and ultimately an increase in the dimensions of the transformer where the tap changer device is installed, which involves use of a larger volume of dielectric fluid, the increase in total weight of the transformer, the need for using an oil leakage sump having a larger dielectric fluid collecting capacity, etc. The dimensions of the transformer are also increased due to the design of the tap changer device, since this device comprises all the means and elements mounted on a vertically arranged longitudinal plate. Furthermore, given that the tap changer device is installed below the upper cover of the transformer, the height of the latter is increased, the transformer cavity where the tap changer device is mounted having to be filled with dielectric fluid.
On the other hand, in this solution of the state of the art the switching means are arranged linearly behind one another and vertically, the switching of which involves vibrations that are not compensated, thereby impairing the mechanical capabilities of the solution. Another example of a solution with the switching means arranged vertically is disclosed in US2014159847A1.
Some solutions with the switching means arranged equidistantly from one another at 120° on a horizontal plane are known. For example, solutions of this type are mentioned in patent documents JPS6091608 and JPS6047405. The solutions of patent documents JPS5687307 and JPS5681915, where the objective is to minimize the volume of the solution with the arrangement of the switching means, can also be mentioned. However all these tubular solutions, conceived for power transformers, have a vertical arrangement which does not allow the efficient integration thereof in distribution transformers.
Furthermore, the Bulgarian patent BG62108 B1 describes an on-load tap changer (OLTC) voltage side of the transformer assembly comprising mounted on a side opening of the transformer tank insulation board on which are stacked circular contact components of the selection of three phases to them.
On the other hand, the U.S. patent application US1863392A describes an electric switch including a shaft, two parallel spaced conductive plates supported on said shaft, means for rotating said plates alternately about said shaft, a movable contact secured to each plate, fixed contacts supported in the paths of said movable contacts, and a fixed contact supported in contact with each of said plates.
In order to check the position in which the tap changer device is located, i.e., in order to verify if the tap changer device is connected with the suitable tap, an inspection window means is conventionally provided. This inspection window means is usually arranged on the upper cover of the high-voltage electrical equipment, being a peep hole, for example, made in said cover, which means that the peep hole must assure tightness of the high-voltage electrical equipment since the latter contains a dielectric fluid. On the other hand, since said peep hole is located on the upper cover of the equipment, sometimes due to the height of the electrical equipment or the arrangement of the low- and high-voltage bushings, it is not possible to look through said peep hole without the aid of some means, such as a ladder, for example, allowing the operator to verify the position of the tap changer device.
Verification of the position in which the tap changer device is located is necessary, for example, when commissioning the high-voltage electrical equipment, or for example in the event of any malfunction in the control panel of the installation making said verification impossible. In this sense, the solution appearing in technical paper SO1-01 of CIRED of May 2014 (“Regulacijski Distributivni Transformator”, by Sanela Carevic, Mario Bakaric, Branimir Cucic and Martina Mikulic) can be mentioned as an example, since the solution considered therein comprises a peep hole on the upper cover of the high-voltage electrical equipment, the view of which is hindered by the low- and high-voltage bushings of the cover of the transformer.
In order for tap changer devices to be efficient and cost-effective, there must be a minimal number of switching means, as well as a minimal number of taps, and there must be a maximal number of transformation ratios obtained, without this entailing a significant variation in the constructive arrangement of the transformer.
On the other hand, cold startup of the high-voltage electrical equipment, such as transformers, for example, involves a particularly serious problem in extreme climates in which the dielectric fluid may even solidify, impeding the correct switching of the on-load tap changer device and putting the integrity of the high-voltage electrical equipment at risk. Auxiliary means outside the high-voltage electrical equipment are normally used in these cases so that the dielectric fluid reaches a minimum operating temperature necessary for correct operation of the on-load tap changer device.